Air cooled internal combustion engine



Oct. 9, 1934. H. BOLAS AIR COOLED INTERNAL COMBUSTION ENGINE Filed Feb. 12, 1951 7 INVENTOR. HHREILD Emma.

BY W

ATTORNEY Patented Oct. 9, 1934 PATENT OFFICE AIR COOLED INTERNAL COMBUSTION ENGINE Harold Bolas, Pawtucket, It. I.

Application February 12, 1931, Serial No. 515,182

8 Claims. (Cl. 123-171) The present invention relates to air-cooled internal combustion engines, particularly for aircraft use, and has for an object to provide an engine in which adequate air cooling may be attained, with high efficiency and satisfactory performance. With air-cooled engines heretofore in use there has been high head resistance and drag, and unequal cooling, and the designs did not lend themselves to stream lining. The

0 extra drag on the machine resulting from the use of air-cooled engines heretofore has tended to preclude their use wherehigh efiiciency and performance were desired, with the result that 'for such purposes water-cooled engines have been used for the most part, particularly as their design permitted the whole engine to be cowled in in stream line form, and the resistance was almost entirely of skin friction type, their being no eddies behind the cylinders to cause head resistance.

It is an object of the invention therefore to provide an air cooled engine which will permit skin friction cooling, at the same time enabling full use of cowling to produce stream lined surfaces. Whilegaining these desirable features, theretofore confined to water cooled engines, it is also proposed to obtain added advantages, in lighter weight, and in a reduction in skin friction required to dissipate the heat because of the higher temperatures of the radiating surface. It should be noted in this connection that the temperature of a water radiator must be below 212 F. at ground level to avoid boiling, while the temperature of an air-cooled cylinder can be as high as 500 F. without experiencing difficulty, and for the same velocity and surface the rate of heat dissipation is proportioned to the difference of temperature between the radiating surface and the cooling air. Hence in an air cooled engine less surface will be required at the same speed of cooling air and, therefore, less skin friction will be experienced.

A further object is to provide an engine taking the cooling air from a position in the slip stream of the propeller, and at a point outwardly from the center where the velocity is highest. Another object is to so direct the air that cold air impinges on the cylinder heads where the temperature is highest, and then carrying the heated air to the base of the cylinders where high dissipation is unnecessary, thus providing more uniform cooling at all points and tending to even temperature and improved efficiency. Another object is to provide a structure in which sharp bends are avoided in the air passage, so that the cooling resistance will be practically of wholly skin friction type.

It is also proposed to provide means for increasing the suction at the outlet side so that the velocity of air over the engine cylinders can be increased and a greater cooling eficiency obtained, and further to provide thermostatically controlled means for regulating the supply of cooling air, so that substantially constant cylinder temperature may be maintained automatically.

With the above and other objects in view an embodiment of the invention is illustrated in the accompanying drawing, and this embodiment will be hereinafter more fully described with reference thereto, and the invention will be finally pointed out in the claims.

In the drawing:

Fig. 1 is a side elevation of an airplane engine according to the present embodiment of the invention. I

Fig. 2 is a longitudinal sectional view taken along the line 2-2 of Fig. 1.

Fig. 3 is a front end view.

Figs. 4 and 5 are schematic views of aircraft showing modified arrangements for carrying the cooling air from the engine.

Similar reference characters indicate corresponding parts throughout the severalfigures of the drawing.

Referring to the drawing, the engine illustrated is of four cylinder in-line inverted type, and comprises generally a crank case 10, and depending cylinders 11, 12, 1-3 and 14 cast in pairs. Fins 15 are formed upon the exterior of the cylinders lengthwise thereof in the direction of the stroke of the pistons, and are carried over the cylinder heads, the fins at the ends of each pair being radial of the head, while those between the ends extend transversely in parallel relation, as indicated by the, dotted lines Fig. 2.

A streamlined housing or cowling 16 is disposed about the cylinder and extends from a point spaced a short distance below the crank case ends of the cylinders to a point substantially below the cylinder heads, its base 17 being inclined downwardly from the rear to the front to provide an air passage beneath the cylinder heads of gradually increasing width toward the front. The rearward end of the base is curved into the rear wall of the housing and is preferably streamlined into the fuselage, as at 18.

The housing 16 is carried forwardly of the cylinders and is faired to provide a streamlined nose, in the lower portion of which, and in line with the air passage below the cylinder heads,

there is provided an opening 19 having vertically arranged shutters 2i) pivotally mounted, as at 21, on their axes, and adapted to be adjusted to completely close said opening and to open it to any desired degree up to substantially full opening. According to my invention the opening 19 is disposed at a point of 'the radius of the propeller 22 where the velocity of the slip stream is highest, this point being considerably outwardly of the center of rotation;

Above the opening 19 there is provided a transverse partition 23 curved at its inner end into a cylindrical jacket Wall 24 connected at its vertical edges to the interior of the housing and closely fitted about the forward fins of the first cylinden.

Jackets 25 conforming to the indenturesbetween the cylinders are secured to the interior of the housing to closely fit about the fins at these points, being closed at *their lower ends. The partition 23 and the closed lower ends of the jackets 25 are in a plane at the lower ends of the straight portions of the fins so that the transverse fin portions extending over the cylinder heads are projected into the air channel. W

The jshutters are adapted to be automatically opened and closed by a thermostat 26 disposed in the upper forward portion of the housing and attached to the first engine cylinder. Suitable linkage of well known type, and indicated generally as 27, connects the thermostat to the shutters, closing them when the cylinder is cold and opening them as it heats.

The rocker arms 28, intake and exhaust manifo1ds29 and 30, and spark plugs 31 extend through the housing 16, so that they are readily accessible. In operation the air is taken from the slip stream of the propeller substantially at the point of highest velocity into the opening 19, and through the converging air passage within the housing, from which it is carried over the cylinder heads and upwardly between the vertically disposed fins, being confined as itpasses about the cylinders by the lacketing. After leaving the fins it passes around the crank case chamber and as shown in Fig. 1 emerges through louvres 32 in the top of the engine cowling. The flow of the cooling air is accomplished without any considerable head resistance and sharp bends are' avoided in the air passage, so that the resistance due to cooling is" substantially reduced to skin friction type. It will be observed that the cold air impinges directly on to the cylinder heads where the temperature is highest, and then flows in its heated state to the base iof the cylinders where high dissipation is less necessary, so that there is substantially uniform cooling at all points. The automatic shutter control insures the proper proportion of air for varying temperatures. The invention permits of complete cowling of the engine so that it lends itself to any desired streamlining.

In Fig. 4 I have shown a duct 33 leading from the engine cowling to the under side of the fuselage at a point where the suction effect may be utilized to draw the air and thus increase its velocity over the cylinders.

In Fig. 5 I have shown a modification in which a duct 34 from the engine cowling is carried to the upper surface of the wing so as to produce a suction for increasing the air velocity over the cylinders.

In certain cases, as for instance in multi-engine machines, where the engines are not installed in the nose of the body, but form independent power units, either in juxtaposition to or wholly clear of the wing or supporting surface, the crankcase, cylinder block and air duct can be separately and completely streamlined to offer the minimum of frontal area and head resistance.

I have illustrated and described preferred and satisfactory embodiments of the invention, but it will be obvious that changes may be made therein within the spirit and scope thereof, as defined in the appended claims.

Having thus described my invention what I claim and desire to secure by Letters Patent is:

1. In combination, an air-cooled internal combustion engine of the inverted cylinder type comprising a cylinder having cooling fins extending longitudinally thereof .and across the cylinder head, a propeller driven by said engine, and air conducting means under the engine having an entrance opening disposed in the slip stream of said propeller and conducting air to said head and upwardly between said fins about said cylinderl V 2. In combination, an air-cooled internal combustijon engine of the inverted cylinder type comprising a cylinder having cooling fins extending longitudinally thereof and across the cylinder head, a propeller driven by said engine for forcing a current of air toward the engine, and air conducting means under the engine having an entrance opening disposed in the slip stream of said propeller outwardly of the center of rotation of said propeller and calculated substantially at the point of highest velocity, and conducting air to said head and upwardly between said fins about said cylinder.

3. In combination, an air-cooled internal combustion engine of the inverted cylinder type comprising a cylinder having cooling fins extending longitudinally thereof, a propeller driven by said engine having its axis at right angles to the difection of said fins, air conducting means under the engine having an entrance opening disposed in the slip stream of said propeller and conducting air upwardly between said fins about said. cylinder, adjustable means adapted to control the entrance of air to said opening, and thermostatic means connected to saidcylinder adapted to automatically control said last mentioned means.

4. In combination, an air-cooled internal combustion engine of the inverted cylinder type comprising a cylinder having cooling fins extending longitudinally thereof and across the cylinder conducting air from the head and upwardly be tween said fins to the base of said cylinder, a propeller driven by said engine having its axis at right angles to direction of said fins for forcing a current of air toward the jacket, and means communicating with said jacket means having an entrance opening disposed in the slip stream of said propeller for conducting the forced current upon the head of the cylinder.

5. In combination, an inverted type air-cooled internal combustion engine of the inverted cylinder type comprising a plurality of in-line cylinders having cooling fins extending longitudinally thereof, jacket means surrounding said cylinders conducting air from the heads upwardly head, "jacket means surrounding said cylinder between said fins to the bases of said cylinders,

a propeller driven by said engine having its axis at right angles to the direction of said fins, and air conducting means communicating with said jacket means extending longitudinally of said engine and converging from front to rear end thereof.

6. In combination, an internal combustion engine of the inverted cylinder type comprising a cylinder having cooling fins extending longitudinally thereof, a propeller driven bysaid engine, and means conducting a current of cooling air upon the heads of the engine cylinders and thence upwardly between said fins toward the crankcase of the engine.-

'7. In combination, an internal combustion engine of the inverted cylinder type comprising a plurality of in-lin cylinders having cooling fins' extending longitudinally thereof, a propeller driven by said engine, and means conducting a current of cooling air rearwardly upon the heads of the cylinders and upwardly between said fins tial temperature equilibrium between the cylinder heads and the crankcase of the engine.

HAROLD, noLAs. 

